1. Technical Field
The present invention relates to ink sets, ink-jet recording methods, and recorded materials, and particularly to an ink set and an ink-jet recording method that allow formation of a coating with a metallic finish and a recorded material having such a coating.
2. Related Art
A coating with a metallic finish on a printed material is formed using, for example, a printing ink containing a gold powder formed of brass microparticles or a silver powder formed of aluminum microparticles as a pigment, or by foil stamping or thermal transfer using metal foil.
A coating formed using a printing ink containing a gold or silver powder, however, has a matt metallic finish and cannot attain a mirror finish because the metal powder used has a large average particle size, namely, 10 to 30 μm. In foil stamping or thermal transfer using metal foil, a smooth metal foil is laminated on an adhesive-coated recording medium and is pressed and thermally fused by heating. This method provides a relatively good finish, although its application is limited to recording media resistant to heat and deformation because the method involves many production steps and the media are exposed to pressure and heat during the production steps.
There have recently been many applications of ink jetting to printing, an example of which is metallic printing. JP-A-2002-179960, for example, discloses a technique of ink-jet printing using an ink composition containing a pigment formed of metal-coated plastic spherical particles. To attain a highly metallic finish, however, the spherical particles must be deformed to a flat shape to provide a smooth surface. According to this technique, therefore, roller pressing and heating must be simultaneously performed. This requires a complicated apparatus or production process and also limits the range of recording media that can be used.
JP-A-2003-292836 and JP-A-2003-306625 disclose techniques using an ink composition in which a colloid of a noble metal such as gold or silver is dispersed. This ink composition, however, cannot attain a metallic finish because the noble metal colloid shows a color originating from plasmon absorption if its particle size is reduced to several to tens of nanometers to ensure sufficient dispersion stability. In this case, a good metallic finish can be attained by drying and heating the coating to fuse the colloid particles. Even though a metallic finish is attained using these techniques, it is difficult to form a highly metallic mirror finish with relative specular glossinesses exceeding 200, 200, and 100 at incident angles of 20°, 60°, and 85°, respectively, over a surface evenly without irregularities. If the particle size is increased to ensure a highly metallic mirror finish, the ink composition has low dispersion stability, and the problem of aggregation and sedimentation cannot be avoided, thus showing a significantly decreased storage life. Furthermore, it is self-evident that the use of a noble metal is disadvantageous in terms of cost; it can only be used for high-value-added applications because it significantly raises the cost of the ink composition.